A super-hard cutting edge is provided to a cutting insert by affixing a hard-metal body, such as a PCBN tip, to what is commonly known as a tool carrier or carrier by means of a brazing material, such as a liquid brazing solder.
Polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN), diamond and diamond composite materials are commonly used to provide the super-hard cutting edge for cutting tools, such as cutting inserts used in metal machining.
Referring now to FIGS. 8 and 9, a conventional tool carrier 100 (also known as a blank) includes a pocket 102 defined by a vertical back wall 102a and a horizontal seating surface 102b, and a brazing notch 104 at the intersection between back wall 102a and the seating surface 102b. The brazing notch 102 is formed with a radius, R, for accommodating brazing material when affixing a cutting tip (not shown) to the tool carrier 100. Typically, the brazing notch 102 has a radius, R, of at least 0.10 mm (0.004 in).
A problem has been observed when the tool carrier 100 is manufactured using an injection molding process. The tool carrier 100 may be made of a cemented carbide material. During the injection molding process, the hot carbide material of the tool carrier 100 shrinks in the mold when contacting the mold surfaces. Because shrinkage is proportional to the dimensions of the tool carrier 100, as shown by the arrows in FIG. 8, the hot carbide material shrinks more in the horizontal direction, which causes stress concentration near the brazing notch 104. In addition, a crack in the tool carrier 100 may occur, due to friction force between the mold (or die) and the tool carrier 100 when hot material is injected into the mold (not shown). As the temperature decreases in the tool carrier 100, the tool carrier 100 begins to shrink. Because the tool carrier 100 shrinks differently in the horizontal and vertical direction, the mold will “drag” the notch portion of the tool carrier 100, thus creating cracks, which is detrimental to the performance of the tool carrier 100.
Another problem has been observed when the cutting tip is affixed to the tool carrier. Typically, a chamfer is formed at the corners of the cutting tip that are adjacent the pocket walls in an attempt to provide sufficient bonding force between the cutting tip and the tool carrier, and to avoid interference between the cutting tip and the tool carrier. Unfortunately, producing the chamfer in the cutting tip increases the manufacturing cost of the cutting insert.
The present invention has been developed in view of the foregoing.